Recovery of metallic wastes from gas-washers for metallurgical furnaces



A. L. GENTER March 1, .1 932.

Fil ed June 6, 1950 2 Sheets-Sheet 1 \A. 1.] 'GENTER March 1, 1932.

2 Sheets-Shee t Filed June 6, 1930 Patented Mar. 1, 1932 I UNITED STATESALBERT L. GENTEB, OF BALTIMORE, MARYIiAND, ASIGNOB TO THE KAY.-

COMPAiNY, BALTIMORE, MARYLAND, A CORPORATION OF PATENT. ,OFFIJCE'RECOVERY or METALLIC WASTES raom GAS-WASHERS ron'mnrnrnuaercan FURNACESApplication filed June 6, 1930. Serial No. 459,503.

This invention relates in general to improvement in recovery ofmetallurgical products from spent washing liquids ofmetallurgical-furnace gas-washers, and more particularly to improvementsin recovery of iron from the spent wash waters of blast-furnacegas-washers.

As is well known, the dust of blast furnace gas contains fine iron ore,coke and lime dust which have been carried by entrainment along with thegases from the furnace. It has been common practice to remove thedustfrom such furnace gases by scrubbing or washing the gases with water toclean the gas for subsequent combustion purposes, and to recover the orefrom the spent ,gas washing liquids by filtering, settling, thickeningor other means for separating the dust suspended in the spentfurnace gaswashing liquids. This gas washing is usually accomplished by passing thegases from the blast furnace upwardly through a suitable tower incontact with a descending flow of water.

Thus practically all of the fine ore dust, and the coke. and lime dustcarried in the un- Washed gas is precipitated by the water and carriedalong therewith out of the scrubbing v apparatus as a sludge. Thetowersare usually so constructed'asto cause the streams of gas and water tofollow tortuous paths. According to some present practices the water ispermitted to flow through the tower in film or spray curtains in contactwith bafliesor-packing material contained therein, the necessaryintimate contact of the gases with the water being achievedthrough theturbulency' of the gases in. their upward passages I and the turbulenc'yof the [water in its downward tortuous flow. In some instances .thetowers are so constructed that the water in its downward course iscausedto flow in j the paths of travel 'of the gases.

From these scrubbing towers or apparatus the spent liquid'slud'ge is ledto the separating means for recovering the suspended iron and othercompounds by filtering, decanta tion, settling or otherwise dewateringthem from the sludge. Practice shows that, the Water from such solidand. liquid separating means, after being freed of its suspended sol-'ids, by such separatin means becomes rusty and turbid even though it hasbeen efiiciently filtered or otherwise treated to substantially clear itof suspended solids. This condiwhich have been introduced into the blastfurnace for reduction purposes and which have been blown out of thefurnace with and entrained by-the gas from such furnaces, it isevident,'-that'such dust in the blast furnace gases will be partiallydepleted in oxygen,

due to the reducing reaetionsin the furnace, and will or may be theferrous oxide condition, H p f- It is well known that ferrous oxides arereadily soluble in the presence of carbon dioxide gas, thus formingsoluble ferrous bicarbonate 7 p Typical blast'furnace gases "conta napproximately the following volumetric percentages of various gases Perceiit Garbon monoxide 23 Carbon dioxide c 12 Methane l 2 gfvydrogeu- 2ater vap or 3 I Nitrogen 58 I As such typical blast furnace gases enterthe gas scrubber at temperatures rangingfrom 250 to 600 F., and due tothe manner of- .contact of the gas with the required to remove thedustfrom the-gas,1t 1s evldent Ferrous-bicarbonate in the presence ofwater and oxygen forms both ferric hydrate [Fe.(OH) and hydrated ferricoxide [Fe O- 2Fe(OH) as a water insoluble precipitate, so that bothreactions will occur,

either individually or simultaneously, in bubbling air through asolution ofv ferrous-bicarbonate in order to supply a surplus of oxygen.Consequently, iron so dissolved in the gas scrubbing Water can beremoved from p solution either by precipitation with chemi cals for suchpurpose, such as caustic soda or lime, or by oxidation of the solubleferrous bicarbonate to insoluble ferric hydroxide, as exemplified by thefollowing equations:

. 2Fe(OH) a +400 2. 4Fe (HCO +O 2Fe O32Fe 3 H2O Wherefore, it isbelieved that the rusty and turbid condition of the sludge afterfiltering is due to the dissolving of iron in the scrubber by the gasWashing liquids which dissolved! puts such iron into the insolublecondition iron, being in solution, is not arrested by but readily passesthrough the filter or other solid and llquid separating means, and issubsequently oxidized slowly by the oxygen. of the air to theferricstate, thereby producing the rusty and turbid condition .of thefiltered waste water from the gas scrubber.

Objects of the present invention are to re-' cover such dissolved ironcompounds as well as the insoluble iron compounds and thereby effect amore complete recovery of the iron compounds from blast furnace gasesand the spent gas-washing liquors therefor; to produce a clear effluentfrom the filtering or. other solid and liquid separating operations, forrecovering the solids'from' such spent gas washing liquors; toaccelerate and thereby hasten the oxidation action and precipitation ofthe dissolved iron compounds; to effect such oxidation and precipitationin the spent liquor before it passes through the filter, or other solidand liquid separating medium, for effecting the recovery of theinsoluble iron compounds and thereby effect separation of the dissolvediron compounds at the same time and by the same separating meansheretofore employed for recovering the insoluble iron compounds; toeffect such oxidation and precipitation by the @relativelysimpleexpedient of aeration with well known liquid aeration means; and theinvention has for further objects such other advantages in operation orresult as may be found to obtain dustrial localities.

the spent sludges from the gas washers for washing gases frommetallurgical furnaces, such as blast furnaces, are subjected totreatment to render insoluble in such liquors the soluble metalcompounds and especially dissolved iron compounds in the spent sludge ofblast-furnace gas-washers, so as thereby to precipitate them fromsolution to suspension in the said liquors. Advantageously, the spentsludges from the blast furnace gaswashers are so'treated by efiectingan. aeration of the sludge to cause an oxidation therein of thedissolved iron compounds, such as ferrous bicarbonates, to insolubleiron com-' ounds, such as ferric hydrate, and the aerated sludgethereafter subjected to a known solid and liquid separating operation toseparate from the liquid of the sludge the iron compounds that wereconverted from soluble to insoluble compoundsby such aeration.Preferably such aeration of the spent sludge from the gas washingoperations hereinbefore described is effected before the spent sludgepasses through the filtering medium, or other solid and liquidseparating medium, heretoalong with the other solids that were alreadyin suspension and saves such dissolved iron along with such previouslysuspended solids in any subsequent dewatering operation used for thepurpose of iron recovery from such,

scrubber eflluents, but also renders the final water from suchdewatering system freer from pollution properties, especially in in-'Further, where water from such blast-furnace gas-scrubbers is to befinally purified for boiler feed purposes, or is to be further treatedby water softening chemicals, thepreliminary aeration treatment of thepresent invention will effect a considerable saving in chemicals thatwould otherwise be employed for elimination of the dissolved ironcompounds.

Still further, the preliminary aeration of the sludges from such gasiwashers has an advantageous effect on' the usual filters throughwhich-the water is separated from the solids of such sludge. It has beenfound in practice that the filtration of such scrubber sludgescontaining dissolved iron compounds 4 results in clogging of the poresof the various filtering media employed, due to the ac-v cidental andfortuitous breaking down of the iron compounds within the pores oftheme- .dium as the clear filtrate passes therethrough. This deposit'ofiron hydrate or oxide in the medium itself soon renders the mediumimpervious. With the aeration of the present I invention preliminarilyto the filtration, the

breaking down and-precipitation of the dis-- ,solved iron compounds isefiected before the" liquid reaches v the filter medium. Consequently,suchhardening effect of the filtering medium is greatly lessened by thepresent invention, and the efliciency and life of the filtion'trough. Itis apparent, however, that.

any other well known aeration means for liquid may be employed in placeof -the aeration trough mentioned, or other means adapted to efiect aprecipitation from solution to '25 suspension ofdissohied' metalcompounds act:

ing similarly to ferrous bicarbonate in s0lution for purposes of theresult obtained with the present invention. o r

In the accompanfying drawings, forming apart of this speci cation'andshowing, for

vention.

and 1 purposes of exemplification, a preferred form and manner inwhich'the invention may-be embodied and practiced, but without limitiing the claimed invention specifically to such illustrative instance orinstances; 1 I Figural is atypical layout of a plant ar ra'ngedtopractice and embody the method and apparatus-of the. present form; f r

Fig. 2 isa top plan view of one form of an aeration tank adapted to beemployed in con? junction with the present invention; n

Fig. 3 is a. side elevational view \of thesame; 1 Fig. 4 is an endelevational view of the same; v l Fig. 5 is a vertical cross-sectionalview' of thesame taken on the lines 5-5 of Fig. 2 3

Fig. 6 is a vertical "cross-sectional view of another form ofaeration'tankadaptedto be employed in connection with the present in- Inits presentrembodirnent, the invention is incorporated in a blastfurnace plant for reducingiron 'ore and, for convenience, the presentdescription will be confined to this use of the invention; features ofthe method and apparatus therefor are, however, capable of othervaluable applications and consequently the invention is not confined tothe described as an illustrative. example.

Referring to the drawings, there are illustrated views of ablast furnaceplant of the type hereinbefore mentioned which embodies a blast furnace10, a cyclone dust arrester '11,

agas washer 12 and a thickener'13. The furnace, washer'and thickener areof usual and well known construction and therefore need not be describedin more detail here; As

shown, the various apparatnsof the plant are provided with the usualconnect ons whereby, as heretoforeoemployed, the gases from the blastfurnace 10 pass through conduit 14a to the dust arrester .11 and thenthrough connections 9 to the gas Washer 12 -to be washed therein withliquid supplied thereto. in the usual manner. From the washer 12 thecleaned gas passes through the outlet 15 to further apparatus forcleaning, storage or use. The spent wash'water or sludge from thescrubber 12 containing 1ron dissolvedin the-wash water while in thewasher l 1 2, as well as the usual insoluble solids, passes through theconduit line 16 leading to the thickener 13 a s heretofore. In thethickener,

which is of the type exemplified in Patent No. 1,716,040, the sludgeisthickened to separate the insoluble'solids from the liquids and theliquid discharged at 19 while the recovered solids are removed at21 forreturn to the blast furnace 10. In accordance with thepresent-invention, there is provided in the conduit line 16 leading fromthescruboer l2 to the thickener 13, an aeration means 22 adapted foraerating the sludge in advance of its. being thickened by the thickener.In

an opening therein so as to form anfoutlet 25 for .flow of sludge fromone compartment 2 to another compartment27 in the trough 23. Thesludgeflowing through the line 6 from the gas washer 12 to the thickener 13enters the compartment 26 of tne aerator at ,28, passes through theopening '25 into the compartment27, and leaves the aerator compartment27a't29. v The aerator 22 is so disposed that the sludge ismaintained t erein up to the top level 31.

In the present stance, the double trough is employed; for purposes ofadvantageously conservmg'lengthwise space required by the fact thatlength must be-provided to give the liquid time for .completlon of theaeration action on the slud e while maintaining a continuous flow. ItJS, however, apparent that a trough in a. single line will serve equallywell for the same essential" purpose of the present invention. Mountedabove the top level 31 for the flowing sludge is an aerator pipeormanlfold 32 having a requisite numberof smaller-verspecific use andspecific embodiment herein 'tical feed branches .33 extending downwardlyinto thecompartments 26, 27,1so as tohave their loweropen-ends'dippingin the sludge of the means. V

Surrounding the manifold 32 and enclosing the upper portions of, thevertical feed,

branches 33 is an inverted trough 35 forming an aeration chamber 30, andhaving its lower edges 36 dipping approximately two or three inchesbelow the top level 31 for the flowing sludge stream. The portions ofthe manifold 32 in the respective compartments 36 and through theliquid.

In the form of the aeration means shown in Fig. 6 the air manifold 32and vertical feed branches 33 are eliminated, and in place thereof thereis submerged below ,the level 31 a horizontal conduit or pipe 32provided with openings 33' and wrapped with rubber covering 37 havingperforations, foraminations, or pores therein. The air, in thisembodiment of the invention, is distributed from the interior of thepipe 32' through the openings 33 and then difi'used as minute.

bubbles, or as finely atomized air, into the flowing sludge by thepore-like openings of the rubber covering.

The spent gas washing sludge from the blast-furnace gas-washer inpassing through the aeration means becomes aerated and as a resultthereof any oxidizable soluble iron compounds that may be present inthesludge are oxidized to the insoluble state. The newly formed ironcompoundsare thereby caused to fall outof solution, and remain as"solids in suspension in the flowing sludge until separated from theliquid content of the sludge by the solid and liquid separating means 13as usually employed heretofore to separate the solids, or insolublecontent, from the liq- -uid of eflluent from thegas washer. As theaerationg is "effected in advance of the separating means 13, it will beapparent that the oxidized soluble iron compounds will be in the samesolid state as the solid matter that has heretofore been separated fromthe liquid by such separating means, and therefore the separation andrecovery of the soluble iron compounds will be eflected' by'the sameapparatus and process steps heretofore employed for the insolublecompounds and heretofore have passed on as filter eflluent;

It will be apparent from the foregoing de-.

scription that the novelfeatures of the present invention are welladapted to advantageous employment with-other types of gas washer andwith other types of dewatering or solid and liquidseparating means andmethods, and that the invention may be advantageously employed inconjunction with" blast or other furnaces for treatment byv reductionofores other than iron ores.

It will also be manifest from the foregoing description thattheoxidizing properties of the air used may be materially augmented bythe introduction into the air used of some ozone, from well knownozonators; and that liquid oxidizing agents also may be advantageouslyadded to the sludge and/or-air current as an aid to the main aeratingaction for accomplishing the novel oxidation of the present invention.

The invention as hereinabove set forth or exemplified may be variouslypracticed or embodied within the scope of the claims hereinafter made.

I claim 1. In the recovery of iron from blast nace gas, the 'methodcomprising washing blast furnace gas with liquid to'remove dust fromsaid gas; aerating the spent gas-wash- 0 ing liquid to oxidize andprecipitate soluble iron compounds dissolved therein; and separating andrecovering the insoluble content from the liquid of the so aerated spentgaswashing liquid.

2. In the recovery of iron from blast furnace gas, the method comprisingwashing blast furnace gas with liquid to remove dust from saidgas;treating the spent gas-washing liquid to oxidize and precipitate solubleiron compounds dissolved therein; and separating and recovering theinsoluble content from the liquid of the so treated spent gas g washingliquid.

3. In amethod of recovering iron from liquid effluent of blast-furnacegas-scrubbers which involves separating and recovering insoluble solidsfrom the liquid of said liquid eflluent, the improvement comprising:aerating said effluent to oxidize and precipitate soluble iron compoundsdissolved therein in advance of said separating and recovering ofinsoluble solids therefrom.

4. In a method of recoveringiron from liquid efiluent of blast-furnacegas-scrubbers which involves separating a'nd recovering insoluble solidsfrom the'liquid of said liquid effluent, the improvement comprising:treatmg said eflluent to oxidize and precipitate soluble iron compoundsdissolved therein in advance of said separating and recovering ofinsoluble solids therefrom.

In the treatment of liquid efliuent from blast-furnace gas-scrubbers,the improve- .through which the soluble iron compounds in iron compoundsdissolved in said eflluent,

and recovering the so oxidized and precipitated ron compounds.

6. In apparatus of the character described,

the combination with a blast-furnace gas- Washer adapted for Washing gasfrom a blast furnace with a Washing liquid, and solid and liquidseparating means adapted for separating solids from liquid of spent Washliquid from said gas-Washer, of an aeration means adapted for aerationof said spent wash liquid, and means for conducting spent liquidfromsaid gas-Washer, to said aeration means, and means for conductingthe aerated liquid from said aeration means to said solid and liquidseparating means.

7. In apparatus for recovering iron from blast furnace gas comprising agas-washer for Washing said blast furnace gas with gas Washing liquid,and solid and liquid separating means adapted for eflecting separationand recovery of solids including iron from spent Washing liquid fromsaid gas-Washer and means for passing said liquid from said gaswvasherto said solid and liquid separating means, the improvement comprisingmeans adapted for aerating the spent Washing liquid that may pass fromsaid Washer to said separating means.

In testimony whereof I have hereunto set my hand.

ALBERT L. GENTER.

